TRUFFLES: WHY PIGS CAN SNIFF THEM OUT

By WALTER SULLIVAN

Published: March 24, 1982

Truffles are rare and expensive as it is. They would be far more so, were it not for the remarkable ability of pigs to sniff them out from as deep as three feet underground.

Why are those animals so capable? Is it related to the omnivorous appetite that has given ''eating like a pig'' so bad a name? And what is the basis for the remarkable appeal of those fungi to gourmets?

The explanation, it seems, relates to the sex life of pigs - and perhaps of human beings as well. Researchers in West Germany have found that truffles contain large quantities of a substance also synthesized in the testes of boars. In the boars it is secreted into their saliva when they court females. The Germans report that the substance's musklike scent, ''emanating from the saliva foam, is smelled by the sow and prompts her standing reflex.''

The chemical is twice as abundant in truffles as in the blood plasma of boars. Furthermore, it and related steroids are produced in the testes of human males and secreted by their armpit sweat glands. It can also be detected in the urine of women.

As reported by the German researchers in the journal Experimentia last year and last month by the journal Science, experiments at the University of Birmingham in England indicate that this substance has a psychological effect on human beings.

Michael Kirk-Smith and his colleagues at that university showed pictures of normally clad women to male and female subjects, some of whom were also exposed to the musky odor of the substance, described chemically as 5a-androst-16-en-3a-ol.

The subjects were asked to grade the photographed women for sexual attractiveness. Those who had sniffed the substance gave higher grades than did the others. Such an effect, it is proposed, might also account for the human predilection for truffles.

The German researchers - R. Claus and H.O. Hoppen of the Technical University in Munich and H. Karg of the Lubeck School of Medicine - noted that such steroids occur in other food plants besides truffles. One, produced in the human testes, is also synthesized in small quantities by celery and parsnips.

The truffles tested were black varieties from Perigord, source of those considered the best by many connoisseurs, and white truffles from Italy.

Growing truffles commercially is difficult since they develop underground and very slowly. They do so usually in association with tree roots, especially those of oaks. Efforts have been made in France to restore the open woodlands where they thrive, but 10 years may elapse before such an area becomes fully productive.

Specially trained dogs, instead of pigs, are sometimes used to seek out the truffles. Where maturing truffles have swelled enough to crack open the ground, swarms of small yellow flies may indicate the location and the odor may be detectable by humans.